TY - JOUR
T1 - Detection of Intrinsic Source Structure at ∼3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A∗
AU - Lu, Ru Sen
AU - Krichbaum, Thomas P.
AU - Roy, Alan L.
AU - Fish, Vincent L.
AU - Doeleman, Sheperd S.
AU - Johnson, Michael D.
AU - Akiyama, Kazunori
AU - Psaltis, Dimitrios
AU - Alef, Walter
AU - Asada, Keiichi
AU - Beaudoin, Christopher
AU - Bertarini, Alessandra
AU - Blackburn, Lindy
AU - Blundell, Ray
AU - Bower, Geoffrey C.
AU - Brinkerink, Christiaan
AU - Broderick, Avery E.
AU - Cappallo, Roger
AU - Crew, Geoffrey B.
AU - Dexter, Jason
AU - Dexter, Matt
AU - Falcke, Heino
AU - Freund, Robert
AU - Friberg, Per
AU - Greer, Christopher H.
AU - Gurwell, Mark A.
AU - Ho, Paul T.P.
AU - Honma, Mareki
AU - Inoue, Makoto
AU - Kim, Junhan
AU - Lamb, James
AU - Lindqvist, Michael
AU - Macmahon, David
AU - Marrone, Daniel P.
AU - Marti-Vidal, Ivan
AU - Menten, Karl M.
AU - Moran, James M.
AU - Nagar, Neil M.
AU - Plambeck, Richard L.
AU - Primiani, Rurik A.
AU - Rogers, Alan E.E.
AU - Ros, Eduardo
AU - Rottmann, Helge
AU - Soohoo, Jason
AU - Spilker, Justin
AU - Stone, Jordan
AU - Strittmatter, Peter
AU - Tilanus, Remo P.J.
AU - Titus, Michael
AU - Vertatschitsch, Laura
AU - Wagner, Jan
AU - Weintroub, Jonathan
AU - Wright, Melvyn
AU - Young, Ken H.
AU - Zensus, J. Anton
AU - Ziurys, Lucy M.
N1 - Funding Information:
We thank the anonymous referee for constructive comments that improved the paper. The authors thank the APEX observatory staff and the APEX team at the MPIfR for their support. In particular, we appreciate the help of R. Güsten, D. Muders, and A. Weiss. R.-S.L. thanks Dr. Lei Chen for fruitful discussion on the data analysis and Dr. R. W. Porcas and Dr. N. R. MacDonald for very useful comments and discussions. K.A. thanks Prof. Koji Hukushima, Prof. Masato Okada, and Dr. Kenji Nagata for useful advice and suggestions on the development of our modeling code using the Exchange Monte Carlo method adopted in this work. H.F. acknowledges funding from the European Research Council (ERC) Synergy Grant “BlackHoleCam” (Grant 610058). E.R. acknowledges support from the Spanish MINECO through grants AYA2012-38491-C02-01 and AYA2015-63939-C2-2-P and from the Generalitat Valenciana grant PROMETEOII/2014/057. Based on observations with the Atacama Pathfinder EXperiment (APEX) telescope (under project ID 091.F-9312(A)). APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The JCMT was operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the UK, the Netherlands Organisation for Scientific Research, and the National Research Council of Canada. Funding for ongoing CARMA development and operations was supported by the NSF and CARMA partner universities. Facility: EHT.
Publisher Copyright:
© 2018. The American Astronomical Society.
PY - 2018/5/20
Y1 - 2018/5/20
N2 - We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A∗, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N-S direction, and leads to a spatial resolution of ∼30 μas (∼3 Schwarzschild radii) for Sgr A∗. The source is detected even at the longest baselines with visibility amplitudes of ∼4%-13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of ∼3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.
AB - We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A∗, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N-S direction, and leads to a spatial resolution of ∼30 μas (∼3 Schwarzschild radii) for Sgr A∗. The source is detected even at the longest baselines with visibility amplitudes of ∼4%-13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of ∼3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.
KW - Galaxy: center
KW - submillimeter: general
KW - techniques: high angular resolution
KW - techniques: interferometric
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U2 - 10.3847/1538-4357/aabe2e
DO - 10.3847/1538-4357/aabe2e
M3 - Article
AN - SCOPUS:85048028220
VL - 859
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 60
ER -